The present invention relates to a magnetic head used for magnetic recording apparatuses such as magnetic disc apparatuses, more particularly to a read-only magnetoresistive thin-film magnetic head for detecting signals recorded in a magnetic recording medium using the magnetoresistive effect unique to a ferromagnetic material, and to a method for fabrication thereof.
A magnetoresistive thin-film magnetic head comprises an upper shield film and a lower shield film formed on a substrate, a magnetoresistive film, a biasing film for applying a biasing magnetic field to the magnetoresistive film, a pair of opposed electrodes electrically connected to a magnetoresistive element, an upper gap film (upper insulating film) formed between the magnetoresistive element and the upper shield film, a lower gap film (lower insulating film) formed between the magnetoresistive element and the lower shield film, and a noise suppression film (magnetic domain controlling film) for controlling the magnetic domain of the magnetoresistive elements.
An example of the prior art relating to the present invention is disclosed in JP-A-3-125311 (reference (1)). The invention disclosed in reference (1) is concerned with a technique for fabricating a magnetoresistive thin-film magnetic head using what is called the lift-off method. More specifically, a magnetoresistive element is formed by ion milling with a resist pattern as a mask according to the lift-off method, after which a hard magnetic film and an electrode are formed, followed by separating the resist pattern by the lift-off method. The invention disclosed in the above-mentioned patent publication is intended to improve the electrical insulation between the lower shield film and the electrode by forming an insulating film before forming the hard magnetic film (noise suppression film). The lower shield film, though not described in the drawings attached to reference (1), is required for reducing the effect of the signals from adjacent tracks at the time of reading-signals from the magnetic recording medium by a magnetoresistive thin-film magnetic head. The lower shield film is an electrical conductive film. The electrode for conducting the current to the magnetoresistive element (MR sensor) is required to be formed into a shape that can secure a predetermined electrical resistance. For this purpose, a part of the electrode is formed in a region other than the hard magnetic film or the magnetoresistive element (MR sensor). An insulating film (lower gap film) is formed between the magnetoresistive element (MR sensor) and the lower shield in order to prevent leakage to the lower shield film of the current supplied to the magnetoresistive element (MR sensor). In similar fashion, another insulating film (upper gap film) is formed between the electrode and the lower shield in order to prevent the leakage from the electrode to the lower shield film. In reference (1), an electrode film is continuously formed after forming a hard magnetic film (noise suppression film).
In a magnetoresistive thin-film magnetic heads electrical insulation is required between a magnetoresistive film, an electrode film and an upper shield film and also between a magnetoresistive film, an electrode film and a lower shield film where the current for detecting magnetic signals flows. A sufficient voltage resistance, i.e., a sufficient dielectric strength between the upper and lower shield films therefore is indispensable for improving the head life and the output of the detection signal.
JP-A-5-54336 (reference (2)) discloses a magnetoresistive thin-film magnetic head comprising an insulating film (gap film) between upper and lower shield films. In spite of this, the same disclosure includes no reference to securing the dielectric strength.
JP-A-59-104721 (reference (3)), JP-A-59-60726 (reference (4)) and JP-A-61-54012 (reference (5)) disclose a structure comprising an insulating layer formed between an upper shield film and an electrode film to improve the dielectric strength between the upper shield film and the electrode films JP-A-4-123307 (reference (6)) discloses a technique intended to prevent the short-circuiting between the upper and lower shield films which otherwise might occur as a result of a reduced thickness of the insulating layer at a misalignment of a connector between a magnetoresistive element and an electrode or the portion of the electrode riding over the magnetoresistive element at the time of depositing an insulating layer. For this purpose, the thickness of the insulating layer at the portions other than the track is increased as compared with that of the insulating layer at the track. Specifically, after the magnetoresistive element on the insulating layer is patterned, another insulating layer is deposited before deposition of an electrode, after which an electrode is deposited thereby to eliminate the electrode misalignment.
JP-A-4-182912 (reference (7)) discloses a technique for preventing an electrode under an upper shield film and an upper insulating layer from being etched to a thinner layer at the time of etching the upper shield film. In order to prevent this inconvenience, a protective film is formed after forming the upper insulating layer, followed by forming the upper shield film. This disclosure indicates that when the upper shield film is etched, the etching of the electrode and the upper insulating layer is prevented.